The present application claims priority to Japanese Application No. P2000-213367 filed Jul. 10, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a printer and a printer driving method. The present invention is, in particular, applicable to an inkjet printer such as a thermal inkjet printer. The present invention makes it possible to reduce graininess using a simple structure as a result of previously adhering diffusion liquid to an ink adhering location, and controlling the amount of diffusion liquid.
2. Description of the Related Art
In recent years, there has been an increasing need for colored hard copies. To respond to this need, inkjet printers, such as continuous-vibration-generating (piezoelectric) inkjet printers and thermal (bubble-jet-type) inkjet printers, are constructed so as to print, for example, a desired image by ejecting ink droplets from a nozzle and adhering them to a print material, and so as to produce a tone gradation based on dot density, the dots being formed by adhering the ink droplets to the print material.
In other words, whereas dark-colored locations are produced by ejecting a large number of ink droplets so as to increase dot density, light colored locations are produced by reducing the number of ink droplets so as to reduce dot density.
However, in inkjet printers, since the tone gradation is produced based on dot density, the intervals between adjacent dots are large in the light-colored regions of the printed result, so that the graininess of the printed result becomes pronounced, thereby resulting in the problem of reduced quality of the printed result.
One method of overcoming this problem involves reducing the sizes of dots to values that cause graininess to be unnoticeable as a result of reducing the sizes of ink droplets. However, for practical purposes, it is difficult to reduce the sizes of ink droplets to values that cause the graininess to be unnoticeable. In addition, when the sizes of ink droplets are reduced, it is necessary to considerably increase dot density at the dark-colored locations, thereby resulting in the problem that nozzles must correspondingly be disposed closer together.
Another method of overcoming this problem involves properly using ink types of different densities at the light-colored locations and the dark-colored locations. In this case, however, two heads are required for one color, so that the structure of the heads become complicated, thereby resulting in the problem of increased costs.
As opposed to this, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 57-109662, diffusion liquid may be adhered to low-density locations of a sheet where dots become sparsely disposed in order to increase the areas of dots and to reduce the density using the diffusion liquid. However, when, as in this method, the areas of the dots at the locations where they become sparsely disposed are increased using the diffusion liquid, the problem of graininess can be overcome for intermediate tones, whereas, for low-density locations, since the dots are made large, the graininess becomes, on the contrary, pronounced, as a result of which, from the practical point of view, the problem of graininess is not satisfactorily solved yet.
Accordingly, in view of the above-described problems, it is an object of the present invention to provide a printer which makes it possible to reduce graininess using a simple structure. It is also an object of the present invention to provide a method of driving the printer.
In the present invention, by controlling the amount of diffusion liquid adhered to one location of a print material and the amount of ink adhered to the one location, it is possible to produce a tone gradation at the one location.
In addition, in the present invention, by controlling the amount of diffusion liquid in a dot formed by the diffusion liquid, it is also possible for the size of the dot to become equal to or greater than a predetermined value as required.
Further, in the present invention, by controlling the amount of diffusion liquid adhered to one location of a print material, and the amount of ink adhered to this location in order to produce a tone gradation at this one location, even when the amount of ink is small, it is possible to increase the size of the dot by the amount of diffusion liquid, and, thus, to decrease the dot density. Therefore, it is possible to reduce graininess. Further, by controlling both the amount of ink and the amount of diffusion liquid, it is possible to control the tone gradation in such a way as to produce a fine tone gradation.
Still further, in the present invention, by controlling the amount of diffusion liquid in the dot formed by the diffusion liquid, the size of the dot formed by the ink is such as to be equal to or greater than a predetermined value as required even when the amounts of ink of the dot differ. Therefore, it is possible to form a dot whose size is equal to or greater than the predetermined value even when the amount of ink is small, so that graininess can be reduced.